The present invention relates to a light-emitting device, and more particularly, to a light-emitting device which can effectively use light from a light-emitting element connected to a wiring substrate.
FIG. 1 is a sectional view illustrating a known light-emitting device.
Referring to FIG. 1, a light-emitting device 100 includes a light-emitting element 101, a sub-mount substrate 102, a board substrate 103, external connection terminals 104 and 105, and a heat-sinking plate 107.
The light-emitting element 101 is an element which emits light from the entire surface thereof. The light-emitting element 101 has power supply terminals 111 and 112. The light-emitting element 101 is connected to the sub-mount substrate 102 in a flip-chip bonding manner.
However, the sub-mount substrate is fixed to the board substrate 103 by the use of a bonding method using an Au—Sn alloy which has thermal conductivity higher than solder. The sub-mount substrate 102 includes a substrate body 114 and wiring patterns 115 and 116. The substrate body 114 serves to mount the wiring patterns 115 and 116 thereon. The substrate body 114 can be made of a material having high thermal conductivity, such as AlN.
The wiring patterns 115 and 116 are formed on the substrate body 114. The wiring pattern 115 is electrically connected to the power supply terminal 111 via a bump 118 and the wiring pattern 116 is electrically connected to the power supply terminal 112 via a bump 118. The sub-mount substrate 102 serves to raise the light-emitting element 101 so as to protrude higher than the top surfaces 104A and 105A of portions of the external connection leads 104 and 105, in which the portions are disposed on the board substrate 103.
In such a configuration, since the light-emitting element 101 is raised to protrude higher than the top surfaces 104A and 105B of the external connection leads 104 and 105 disposed on the board substrate 103, it is therefore possible to effectively use light emitted from the entire surface of the light-emitting element 101.
The board substrate 103 includes a substrate body 121 and wiring patterns 122 and 123. The substrate body 121 serves to mount the wiring patterns 122 and 123 thereon. The substrate body 121 can be made of a material having high thermal conductivity, such as AlN or ceramic. The wiring patterns 122 and 123 are disposed on the substrate body 121. The wiring pattern 122 is electrically connected to the wiring pattern 115 via a wire 125A. The wiring pattern 123 is electrically connected to the wiring pattern 116 via a wire 125B. That is, the sub-mount substrate 102 is connected to the board substrate 103 in a wire bonding manner.
The external connection terminal 104 is fixed onto the wiring pattern 122 using Ag paste 127 as an adhesive. The external connection lead 105 is fixed onto the wiring pattern 123 using the Ag paste 127 as an adhesive.
The heat-sinking plate 107 is fixed onto the bottom surface of the substrate body 121 by using Ag paste. The heat-sinking plate 107 serves to release heat, which is generated when the light-emitting element 101 emits light, outside the light-emitting device 100. The heat which is generated when the light-emitting element 101 emits light is transmitted to the heat-sinking plate 107 via the sub-mount substrate 102 and the board substrate 103 (see Patent Document 1).
[Patent Document 1]
Unexamined Japanese Patent Application Publication No. 2005-203448
However, the related-art light-emitting device 100 has a problem with increase in cost because the sub-mount substrate 102 is fixed to the board substrate 103 using an expensive material of an Au—Sn alloy by the use of an Au—Sn bonding method.